1. Field of the Invention
The present invention relates to a radiation temperature measuring method and a radiation temperature measuring system to be applied to, for example, the temperature of a semiconductor wafer.
2. Description of the Related Art
A single-wafer heating apparatus is one of heating apparatus for heat-treating semiconductor wafers. Such a heating apparatus heats a wafer for an annealing process by heat generated by heating lamps. To anneal a wafer in a high intrasurface uniformity, it is necessary to measure the temperature of the wafer, and to regulate the temperatures of the heating lamps on the basis of measured temperature in a feedforward or feedback control mode. Some methods of measuring the temperature of the wafer use a radiation thermometer.
These methods measure the emissivity of the wafer and determine the temperature of the wafer on the basis of the emissivity and measured intensity of radiation emitted by the wafer. Methods of measuring the emissivity are classified roughly into two methods. In one type of methods, light having a known wavelength and a known intensity is emitted, then reflected light from the surface of the wafer is detected to determine the emissivity. In the other type of methods, radiation emitted by the wafer is subjected to multiple reflection, then reflected radiation is detected in a plurality of environments respectively having different geometric factors, then the emissivity is calculated on the basis of a plurality of data.
A temperature measured by any one of those methods includes a measuring error caused by a loss due to the scattering of the reflected light outside a probe principally owing to scattering on the measuring surface of the wafer, and noise caused by the unnecessary detection of light emitted by the heating lamps. Therefore, the probe must be set very close to the measuring surface of the wafer, i.e., the probe must be set at a position at 0.5 to 5 mm from the measuring surface of the wafer, to suppress the effect of those causes of measuring error. Such a requirement with the probe places significant restrictions on the design of the radiation thermometer and there is the possibility that the probe affects adversely to the uniform heating of the wafer.
U.S. Pat. No. 5,660,472 discloses a correcting technique for measurement employing a virtual blackbody included in a multiple reflection system. Basically, this correcting technique is practiced as follows. As shown in FIG. 13, the measuring system includes, as basic components, a wafer W, a reflecting plate (bottom wall of a vessel) 101, and first and second probes (two sapphire rods) 102. The temperature of the wafer W is measured by the following procedure.
(i) The first probe 102 of a diameter dp is inserted in a first aperture of a diameter d1 (d1 greater than dp) formed in the reflecting plate 101.
(ii) Since the aperture of the finite size exists when virtual blackbody cavity is formed, reflected light is reduced by an amount. Therefore, an effective reflectivity R1 is determined taking into consideration a decrement in reflected light.
(iii) The second probe 102 of a diameter dp is inserted in a second aperture of a diameter d2 (d2 greater than dp) formed beside the first hole.
(iv) An effective reflectivity R2 is determined taking into consideration a decrement in reflectivity.
(v) The reflectivities R1 and R2, measured temperatures T1 and T2 measured respectively by the probes 102 are substituted into a specific equation to calculate the temperature of the wafer.
The foregoing correcting technique has the following problems:
{circle around (1)} Basically, the virtual blackbody is composed of a flat plate of an infinite dimensions, however, the characteristics of the virtual blackbody is spoiled by the two apertures formed therein for the probes.
{circle around (2)} Normally, the reflectivity of the virtual blackbody is not affected by the emissivity of the wafer. As obvious from the fact that the virtual black body takes the effective reflectivities into consideration, the reflectivity of the reflecting plate 101 is not xe2x80x9c1xe2x80x9d; that is, the reflectivity of the reflecting plate 101 is affected to the emissivity of the wafer, so that accurate measurement of thermal emissive cannot be achieved.
{circle around (3)} The radiation thermometer cannot measure low temperatures.
The present invention has been made to solve the foregoing problems and it is therefore an object of the present invention to provide a radiation temperature measuring method capable of measuring the temperature of a measuring object in a high accuracy by using a multiple reflection system.
Another object of the present invention is to provide a radiation temperature measuring system suitable for carrying out the radiation temperature measuring method.
According to a first aspect of the present invention, a radiation temperature measuring method is provided, which determines the temperature of a flat measuring surface of a measuring object on the basis of a measured radiation intensity obtained by using an optical reflector having a flat reflecting surface narrower than the measuring surface and disposed with the reflecting surface thereof facing the measuring surface, and optical path extending through the optical reflector and respectively having an exposed light-receiving plane surrounded by the reflecting surface, and by receiving radiation undergone multiple reflection between the measuring surface and the reflecting surface through the light-receiving plane of the optical path. The method including the following steps:
(a) setting four combinations of measuring conditions (S1, d1), (S1, d2) (S2, d1) and (S2, d2), where S1 and S2 are the areas S of the reflecting surfaces, and d1 and d2 are distances d between the reflecting surfaces and the measuring surface, and measuring radiation intensities Esid1, Es1d2, Es2d1 and Es2d2 for the four combinations;
(b) substituting the areas S, and an area of a side surface of a cylindrical space between the reflecting surface and the measuring surface (a product of perimeter D of the reflecting surface and the distance d) and the measured radiation intensity E into an expression:   E  =                              ϵ          ⁢                      xe2x80x83                    ⁢                      E            0                                    1          -                      R            ⁢                          xe2x80x83                        ⁢                          (                              1                -                ϵ                            )                                          ·      S        +                  D        ·        d            ⁢              xe2x80x83            ⁢              (                              E            N1                    -                      E            L1                          )              +          (                        E          N2                -                  E          L2                    )      
where xcex5 is an emissivity of the measuring surface, E0 is a blackbody radiation intensity at a temperature T, R is a reflectivity of the reflecting surface, EN1xe2x88x92EL1 is a correction for correcting an error due to noise entering and leaking from the cylindrical space between the reflecting surface and the measuring surface, and EN2xe2x88x92EL2 is a correction for correcting an error due to noise entering and leaking from the space between the reflector and the optical path, to calculate EN2xe2x88x92EL2 for each of the four combinations;
(c) substituting calculated EN2xe2x88x92EL2 into the expression, setting two combinations of measuring conditions of the area S and the distance d, the two combinations being different from each other, measuring radiation intensities for the two combinations, and substituting the measured radiation intensities into the expression to determine EN1xe2x88x92EL1;
(d) correcting the measured radiation intensity on the basis of the expression into which EN1xe2x88x92EL1 and EN2xe2x88x92EL2 are substituted;
(e) calculating the emissivity of the measuring surface on the basis of a measured radiation intensity measured with the reflector removed and the corrected measured radiation intensity corrected in step (d); and
(f) determining temperature of the measuring surface on the basis of the emissivity of the measuring surface and the measured radiation intensity measured with the reflector removed.
The two combinations used in step (c) may be selected from the combinations in step (a).
According to a second aspect of the present invention, a radiation temperature measuring system for measuring the temperature of a flat measuring surface of a measuring object comprises: a rotating plate disposed opposite to the measuring surface; at least five sets of light-receiving parts P1 to P5 disposed in a circumferential arrangement on the rotating plate and smaller than the measuring surface; at least five optical path forming members disposed in a space between the measuring surface and the rotating plate opposite to the measuring surface so as to correspond to the light-receiving parts P1 to P5; and a radiation intensity measuring unit for measuring the respective intensities of radiation passed the light-receiving parts disposed on the rotating plate.
Each of the light-receiving parts P1 has a through hole, and each of the light-receiving parts P2 to P5 has a reflector having a flat reflecting surface facing the measuring surface and provided with a through hole formed therein in a direction along the thickness of the rotating plate and having one end opening in the reflecting surface. The areas of the reflecting surfaces of the light-receiving parts P2 and P3 are S1 and those of the light-receiving parts P4 and P5 are S2. The distance between the reflecting surface of the light-receiving parts P2 and the measuring surface and the distance between the reflecting surface of the light-receiving part P3 and the measuring surface are D1 and D2, respectively, and the distance between the reflecting surface of the light-receiving parts P4 and the measuring surface and the distance between the reflecting surface of the light-receiving part P5 and the measuring surface are D1 and D2, respectively. The rotating plate is rotated to locate the light-receiving parts P1 to P5 sequentially opposite to the optical path forming members, and the emissivity of the measuring surface is determined on the basis of radiation intensities measured by the radiation intensity measuring unit.
In this radiation temperature measuring system, it is preferable to cover a space through which the radiation leaving the exit ends of the light-receiving parts travels with a black cover. It is preferable that the radiation intensity measuring unit is capable of collectively measuring errors caused by the radiation leaving the light-receiving parts as two-dimensional data.